1. Introduction
This invention relates to treatment of a condition known as dry eye and more particularly, to the treatment of dry eye by topical application of certain charged phospholipids to the ocular surface.
2. Description of the Prior Art
It is known that dry eye is a condition of the eye and or the adnexa that usually causes a feeling of discomfort such as ocular dryness, grittiness, burning, soreness or scratching, dependent upon the subject and his condition. Many theories have been offered to explain the possible causes of dry eye. These theories range from the simple to the complex and include inadequate Meibomian gland secretion, insufficient tear volume, mucous deficiency, evaporative losses from the tear film and failure to form an adequate tear film. Proposed causes for dry eye, treatment and symptoms are all described in a compendium of papers on the subject edited by Holly, The Preocular Tear Film In Health, Disease, and Contact Lens Wear, The Dry Eye Institute, Lubock, Texas, 1986, incorporated herein by reference.
The most common treatment for dry eye involves alleviation of dry eye sumptoms by topical application of a tear substitute that adds a volume of liquid to the anterior surface of the eye and related adnexa. Typical tear substitute compositions comprise water soluble, aqueous polymer compositions. Such compositions include, for example, saline solutions of polyvinyl alcohols, hydroxypropylmethyl celluloses or carboxymethyl celluloses. U.S. Pat. No. 4,421,748 teaches an artificial tear composition comprising an aqueous hypotonic solution of lecithin and a viscosity adjusting agent such as a solution soluble cellulose.
Methods used to quantify the effectiveness of tear substitutes for dry eye treatment solutions have not been standardized, and many methods used in the art to quantify the results obtained with such tear-substitute compositions are often inaccurate. For this reason, it is known that reported relief of dry eye symptoms using known tear substitutes varies considerably from subject to subject, and regardless of the method used to quantify relief using a tear substitute, relief often does not exceed several minutes.
The symptoms associated with dry eye are often exacerbated with subjects using contact lenses. In some cases, contact lens intolerance is caused in part or in total by the condition of dry eye and the symptoms thereof. For many subjects, contact lens intolerance is not overcome by topical application of tear substitutes.
For the reasons given above, there is a need for improved compositions and processes for dry eye treatment. In particular, there is a need for a dry-eye-treatment composition that is easy to use, that provides a longer period of relief from dry eye symptoms, and which permits use of contact lenses by subjects having an intolerance to contact lens use due to a dry eye condition or symptoms.